1. Field of the Invention
The present invention relates to a foamed rubber member which is particularly suitably employed as a paper-feeding/conveying roller employed for feeding/conveying paper sheets in office automation apparatuses such as copying machines, facsimile machines, and printers; and as a charge-imparting roller, a transfer roller, a developing roller, a conductive roller, etc. in image-forming apparatuses.
2. Background Art
Transfer/development rollers and paper-feeding/conveying rollers for use in various office automation apparatuses are requested to be low hardness, in order to prevent damage to members which contact the rollers (e.g., a photoreceptor) Hitherto, such rollers have been formed from EPDM rubber (see, for example, Japanese Patent Application Laid-Open (kokai) Nos. 5-77508 and 7-242779). However, as disclosed in the Patent Documents, for producing solid-rubber rollers having low hardness, a softening agent must be added in a large amount to base rubber. The softening agent in such a large amount may cause staining due to bleeding out of the agent and may result in poor durability of the rollers, both of which are problematic.
Meanwhile, use of a sponge roller (i.e., roller made of a foamed material) is another approach to reduce hardness. Such a sponge roller is advantageous in that the hardness thereof can be readily reduced, that the weight thereof can be reduced, and that paper dust adhering resistance on the sponge roller can be prevented. However, when a sponge roller is operated for a long period of time, in some cases, image failures occur (in the case of transfer/development rollers) and conveying performance is impaired (paper-feeding/conveying rollers), both of which are problematic.
Japanese Patent Application Laid-Open (kokai) No. 2008-15008 discloses a toner-supplying roller having a urethane foam surface layer which has been impregnated, through coating, with an isocyanate compound. The disclosed roller has low hardness, and bleeding of an unreacted polyol component is not observed. However, further improvement is required in the durability of the roller.